1. Field of the Invention
The present invention relates to a position detector and an exposure apparatus.
2. Description of the Related Art
A position detector for an exposure apparatus is known and uses a planer encoder that includes a scale (grating) and an encoder head to detect a position of a substrate stage configured to support and drive a substrate (Japanese Patent Laid-Open Nos. (“JPs”) 7-270122 and 2007-266581). One of the scale and the encoder head is fixed onto the substrate stage as a movable member and the other is fixed onto a fixed member. The encoder head usually includes a light source, a grating, and an optical sensor. Light from the light source is deflected by the grating in the encoder head, and reflected and deflected by the scale, and forms an interference pattern on the optical sensor. A position of the substrate stage is detectable by measuring the interference pattern.
The position detector of JP 7-270122 measures the scale by changing a plurality of encoders, and has a problem in that errors accumulate at the switching time. The position detector of JP 2007-266581 has a problem in that the detection precision lowers without calibrations because of the low manufacture precision and low installation precision of the scale. In addition, a quick calibration method is not proposed and the detection needs a long time. Moreover, the detection precision is low because of the low alignment precision between the grating in the encoder head and the substrate stage.